Wiskott-Aldrich Syndrome (WAS) is an X-linked recessive disease characterized by severe immunodeficiency, eczema, recurrent pyogenic infections, and severe thrombocytopenia with small deformed platelets. Patients with WAS have a decreased antibody response to carbohydrate antigens, and a reduced number of T-lymphocytes with impaired functions. The membrane glycoproteins gp1b in platelets and sialophorin (CD43) in T lymphocytes are structurally unstable in patients with this condition. only males are affected, and death may occur in the first decade of life from infection, hemorrhage or malignancy. Heterozygous females are clinically normal and can be identified by pedigree analysis or non-random inactivation of the X chromosome carrying the WAS gene. Although efforts have been expended in recent years by a number of investigators, the underlying intrinsic molecular defects of WAS have yet to be elucidated. By using linkage analysis on restriction fragment length polymorphic (RFLP) markers to study families with this disorder, we have assigned the WAS gene to between two flanking markers, TIMP and DXS255 on Xpll.22-Xpll.3 subregion of 1.8 cM. We will use a variety of fingerprinting techniques to refine the WAS map. These include the study of polymorphic (CA)n repeats and denaturing gel electrophoresis to increase the number of DNA markers and to more precisely map the gene. Cosmid and yeast artificial chromosome libraries will be utilized, these provide valuable resources for high resolution mapping over short distances of the X chromosome. Restriction endonuclease digests of genomic DNA from afflicted individuals will be analyzed on pulse field gradient gel electrophoresis and screened with tightly linked polymorphic probes for structural anomalies. Once firm linkages are established, tightly linked DNA probes should permit accurate carrier detection and prenatal diagnosis of the disease locus. Ultimately, the work described here should lead to the identification of the defective gene and its putative transcript(s), and to a better understanding of the molecular and cellular defects in WAS patients.